1. Field of the Invention
The present invention relates to an electronic musical instrument, such as the electronic piano, which performs musical tone processings by use of one or more digital-signal processing units.
2. Prior Art
Some of the well-known electronic musical instruments (e.g., electronic piano) perform several kinds of interrupting operations and processes such as the key-scan operation for the detection of the depressed key, control operation of the sound source circuit for the generation of the musical tone signal responsive to the key-depression Information, and tone-generation assigning processes. Particularly, some of the recently developed electronic musical instruments must deal with a considerable amount of information as tile number of their additional functions are increased, so that a high-speed processing must be required. In order to embody such demand, the electronic musical instrument is developed such that a large amount of information can be processed at a high speed by the provision of plural processing units.
Such kind of electronic musical instrument provides two central processing units (i.e., CPUs) and a time-division control unit, for example. Herein, the first CPU performs the detecting operation for the depressed keys and the switching operations made on several kinds of panel switches, while the second CPU controls the sound source circuit so as to synthesize the musical tones on the basis of the data supplied from the first CPU. The time-division control unit performs a switching operation on the first and second CPUs at tile predetermined timings. Such electronic musical instrument is designed such that one of two CPUs occupies the data bus.
According to the above-mentioned configuration, the processing functions are shared by two CPUs. For this reason, it is possible to improve the processing speed of the instrument as a whole, and it is also possible to raise the performability of the instrument. This kind of electronic musical instrument is disclosed in Japanese Patent Laid-Open Publication No. 2-257198. Incidentally, it is possible to modify the above-mentioned electronic musical instrument, providing plural CPUs, such that the CPUs each connected with the individual data bus can perform the data transmission via the parallel input/output port.
As described above, the conventional electronic musical instrument provides plural CPUs and performs the time-division control so that one of plural CPUs occupies the data bus. In such configuration, when one CPU occupies the data bus, the other CPU must be in a standby state. In other words, both of the CPUs cannot use the data bus simultaneously, with the result that the usage efficiency of the CPUs cannot be increased. In the modified example of the conventional electronic musical instrument in which the CPUs each having a specific data bus perform the data transmission via the parallel input/output port, there occurs another drawback in that the data transmission speed must be limited and the data sharing cannot be achieved.